Hello there,
We have a forced hot air variable speed furnace. We just had an HVAC company
put 3 heating vents and 2 returns in our finished basement. The basement is
about 1000 sq.ft. We have been told that our furnace should be sufficient to
heat the basement. However, we have a very cool basement. The heat ducts are
on the exterior wall at the floor and the returns are on the same wall but
near the ceiling. We thought the returns should be on the floor since cold
air sinks. Our HVAC guys argue that the returns are on the top of the wall
to create airflow/air pressure. Are they correct? We no longer trust their
judgement since our basement is so cold, but they are willing to come back
and make adjustments. Where should the returns be? Also, would it help to
cut additional heat vents out of the main duct on the ceiling? What do you
suggest they do? Thanks so much for your time.

I think they did it backwards, myself. If the returns are above the
supply, then the warm air can just come out of the vents, up the wall,
and through the returns, never touching the rest of the basement.
That only works if they do *ALL* the walls, so that the
basement is in an envelope of warm air. If they can swap the
returns and supply, that's one way to fix it.